1. Field of the Invention
The present invention relates to a near-field light emitting device and a data recording/reproduction apparatus provided with the near-field light emitting device.
2. Description of the Related Art
With increase of information to be handled, information recording methods and information recording/reproduction apparatuses that can dramatically enhance the recording density are in increasing demand. To increase the recording density, a near-field light that forms a beam spot that is even smaller than a wavelength of an incident light is attracting attention.
The near-field light can be used in optical disk. Investigation, however, on how near-field light can be applied in a magnetic recording apparatus is ongoing. To increase the recording density of a magnetic recording medium, it is necessary that the magnetic recording medium be formed with a magnetically stable material. However, a magnetically stable material makes it difficult to write information on the magnetic recording medium. Therefore, a recording method known as heat (light)-assisted recording method has currently come to be studied.
Heat-assisted recording method involves increasing the temperature at a portion in which information is to be written by applying a beam, temporarily making the portion easily writable, before information is written on the magnetic recording medium by the magnetic head. A recording density of over 1 terabit per square inch (Tbpsi) is expected to be realized by applying near-field light in the heat-assisted recording method.
In the heat-assisted recording method, it is important to make a distance between a magnetic core of the magnetic head and the beam spot short. If the distance is long, the temperature of the portion comes down, making it difficult to write information on the magnetic recording medium.
In a technology disclosed in, for example, Japanese Patent Application No. 2004-255732, the beam outlet is arranged close to the magnetic head. In this technology, a device that emits the near-field light is formed on the same wafer as the magnetic head by lithography. Moreover, a multilayer structure of the near-field light emitting device is made asymmetrical to bring the beam outlet closer to the magnetic head.
However, in the above technology, a thickness of a cladding of an optical waveguide that propagates the laser to the device is not considered. The cladding covers the core of the optical waveguide and is essential for the laser to be propagated to the device without attenuation. The thickness of the cladding should be about the wavelength of the laser. Therefore, the magnetic head and the beam spot are separated by a distance equivalent to the thickness of the cladding.
If the thickness of the cladding is reduced to less than the wavelength of the laser, when the laser comes in contact with a material that is thinner than the cladding thickness and that has a higher absorption coefficient, such as a material used for the magnetic head, absorption occurs on the surface, resulting in attenuation of the laser. Furthermore, absorption of the laser generates heat, resulting in degradation of the magnetic head.